Aquarium Controller

Another project I have in mind is automating planted freshwater aquariums, including timer control of lights and C02 injection, autodosing of fertilizers, and temperature montoring. I want to build a fairly modular system to do this as I imagine that as I get further in to the hobby I may want to extend functionality of the controller, as well as different tanks (I have a small 6 gallon tank at the office) will have different needs.